Analysis of torque ripple in BLDC motor with commutation time

Torque ripple generated in the commutation period is the main drawback of the brushless DC (BLDC) motor, which deteriorates its precision. Many methods to solve this problem have been studied. In many control methods, torque ripple reduction was considered at the point of current control, which means that if current can be controlled properly, the BLDC motor does not produce any torque ripple. In this paper, the authors propose that torque ripple in the commutation period of a BLDC motor is inevitable, even if the current control is successful. A torque model, considered with decaying phase back EMF, is introduced and the causes of commutation torque are analyzed. The influence of commutation time on torque ripple and the relationship between commutation time and speed are introduced. This paper deals with torque ripple reduction of a BLDC motor from the viewpoint of commutation time and gives a theoretical background to reduce it.